Sensing platform design for faecal indicator bacterial detection in recreational waters

Faecal indicator detection in recreational waters is of growing importance in Europe and the rest of the developed world for the safeguarding of the health of users. The EU Bathing Water Directive (BWD) dictates the microbiological water quality standards for European waters using the Faecal indicators: Escherichia coli (E. coli), and Enterococci. Waters are classified as ‘Excellent’, ‘Good’ or ‘Sufficient’. To measure compliance, culture- based tests are widely used and accepted e.g. Colilert 18 from IDEXX or membrane filtration. These methods are reliable and proven but they are slow, typically taking 18 .hours or more to produce a result. These are limited to detecting only Viable-Culturable (VC) cells but not Viable-But-Not-Culturable (VBNC) cells. More rapid results incorporating VBNC detection would allow for more timely and accurate decision- making by governing bodies. This thesis investigates the use of rapid assays based on enzymatic detection to allow for sub 4 hour quantification of E.coli and Enterococci in recreational waters. The work involved improving upon existing enzymatic assays through the introduction of novel reagents and the development of field portable instrumentation for On-site analysis of samples. In this work an enzyme assay for E.coli detection based on β-Glucoronidase activity and the fluorescent substrate 6-Chloro-4-Methylumbelliferone-β-D-glucuronide (6-CMug) was developed. 6-CMug is only recently available (2010) and offered higher fluorescence yield and lower pH sensitivity than previously available substrates such as 4- Methylumbelliferone-β-D-glucuronide (4-Mug). The assay developed offered significant improvements in speed, LOD and sensitivity over existing assays based on 4-Mug. As there is no specific enzyme for the detection of Enterococci culture based assays with specific media were also investigated and a number of detection methodologies were developed. A sensitive field-portable fluorimeter with incubating capability and triplicate sample chambers was designed and built for the on-site analysis of water samples. This development moved beyond state of the art, which was based upon laboratory fluorimeters. The system named ColiSense 1 was designed to conduct a continuous direct enzyme assay for E.coli where the cells were filtered and lysed to release β- Glucuronidase. Data from a one day field trial demonstrated the ability of the system to deliver results on-site within a 75 minute period

Comparison of fluorogenic substrates for the detection of faecal indicator bacteria in water samples using a continuous fluorometric assay.

At present standard methods employed for the microbiological monitoring of bathing waters require at least 18 hours to perform and are based on culturing techniques. This is a huge drawback when immediate action is required. Real-time and on-line monitoring are key factors for consideration in current method development for continuous indicator organism detection in order to meet early warning requirements and water safety plans. Methods utilising β-D-Glucuronidase (GUD) activity as an indicator of Escherichia Coli presence use labelled glucuronides to produce optical signals. Fluorometric assays for the measurement of Escherichia Coli GUD activity are traditionally performed using the fluorogenic substrate 4-methyl-umbelliferone-β-D-glucuronide (4-MUG) which upon hydrolysis releases the fluorophore 4-methyl-umbelliferone (4-MU). The major drawback of 4-MU is its high pKa (7.8), which causes only partial dissociation at pHs around the optimum pH for GUD activity (6.5-7.0). To overcome this issue researchers have employed discontinuous enzyme assays which require the addition of alkali. In this context we explore the spectrophotometric properties of three fluorogenic substrates and their respective aglycons (Fig.1 ) for the continuous measurement of GUD activity and we apply the developed method for the rapid detection of Escherichia Coli in environmental water samples

An affordable smart sensor network for water level management in a catchment

Accurately monitoring water levels at high special and temporal scale is the key element in every catchment or flood risk management system. Building, evaluating and testing hydrological models typically require years of high frequency datasets. Current water level monitoring systems are expensive and usually deployed sparsely throughout a catchment. This may not provide sufficient information to simulate the hydrological variations of a catchment. In this paper, we evaluate the Kingspan Sonic SignalMan ultra-sonic sensor that is designed for monitoring liquid, such as diesel, AdBlue, lubricants additives etc., level autonomously over years. The cost of this sensor is relatively low, which enables the deploying of a water level monitoring system at a much larger spatial scale at an affordable cost. A smart sensor network for catchment management is proposed based on the use of the Kingspan sensor

Autonomous sensors for nutrient monitoring

Cultural eutrophication is the process whereby a body of water becomes over-enriched with nutrients, in particular nitrogen (N) and phosphorus (P), resulting in algal blooms and subsequent death and decomposition which deplete oxygen levels in the water (i.e. hypoxia), leading to the loss of aquatic animals (e.g. fishes). This is caused by excess N and P. Agriculture is the major source to Irish rivers and estuaries, with 70% of P loads and 82% of N loads attributed to agricultural sources . Hypoxia in the Gulf of Mexico has been linked to excessive N loading. Nuisance algal blooms in Lake Erie have been linked to agricultural P. Previous efforts have concentrated on measuring agricultural runoff directly using grab samples or spot measurements, but high frequency sampling will be essential to accurately characterize the extent and temporal resolution of agricultural impacts. Low cost real-time nutrient sensors are critical for quantifying the influence of agriculture on freshwater, and more broadly, for effective water management throughout Irish, European, and American river basins

An optical colour sensor to monitor the marine environment

This research aims to develop a flexible, simple, low-cost, robust, deployable sensor with anti- fouling measures to detect colour change in marine environments. Such a sensor could be used to detect events, inform sampling regimes in coastal areas and act as a qualitative decision support tool. This is useful to decision makers in cities, coastal areas and globally and as gathering data can be expensive using commercial instruments a low cost sensor enables more data to be collected with a better spatial range and resolution. Detecting colour change in water could give warning of events like green tides, e.g. (right) in QuingDao, China, often caused by cyanobacteria

Design features for enhancing optical detection on lab-on-a-disc platforms

Centrifugal microfluidics has undergone a massive growth surge over the past 15 years, evident by the number of comprehensive reviews currently available, with special regard towards Lab-On-A-Disc (LOAD) diagnostic solutions.1–3 The potential of a LOAD system is dependent on its ability to mimic the specific laboratory protocols with which are required to conduct sample-to-answer analysis. This would include sample handling and manipulation (such as mixing and separation), sample modification (including heating and redox reactions), as well as reaction detection (such as optical, electrochemical, or as required by user). Optical detection strategies on LOAD platforms has been largely successful in both the fields of biological and chemical sensing.4 Herein, will demonstrate the optical optimisations which were carried out on a biological fluorescent-based5 and a chemical absorbance-based6 LOAD detection platforms. This will include the identification and optimisation of LED-photodiode selection, the effects of detection orientation and pathway-length fluorophore selection. Also covered will be a comparison between the microfluidic architecture for incorporating either detection methods as well as their reported limits of detection

A novel optical sensing lab-on-a-disc platform for chromium speciation

The determination chromium speciation in the field is a significant analytical challenge. While chromium exists in oxidation states from 0 to VI, it is predominantly found in the (III) and (VI) states [1]. Industry effluent (e.g. textile/electroplating) is a common source of chromium pollution in the environment. Due to corrosion inhibitors used in pipes, and contamination leaching from sanitary landfills, drinking water supplies can become contaminated also [2]. The bioavailability and toxicity of chromium is largely dependent the oxidation state of the element [2]. Consumption of Cr (III) is an essential component in human diet, as it is responsible for maintaining glucose, lipid and protein metabolism [3]. In contrast, Cr (VI) is strongly oxidizing, exhibiting high toxicity, with carcinogenic and mutagenic properties [4]. It is recommended by the World Health Organisation (WHO) that the maximum allowable concentration of chromium (VI) in drinking water is 0.05 mg L−1 [5]. Handheld colourimeters for on-site measurements are a convenient option for frequent water monitoring; however the limit of detection (LOD) of these devices is typically higher than the recommended limit. Microfluidic ‘lab-on-a-disc’ technologies were used in the development of an optical sensor for chromium speciation in water. The principal behind these devices is to minimize laboratory processes onto a microfluidic system that can be brought to the sampling site for rapid sample-to-answer analyses. The objective for this device was to design and fabricate a fully integrated optical sensor for on-site measurement of both trivalent and hexavalent chromium in freshwater. A strong focus was placed on maximizing sensitivity in order to achieve a low LOD

Improving data driven decision making through integration of environmental sensing technologies

Coastal and estuarine zones contain vital and increasingly exploited resources. Traditional uses in these areas (transport, fishing, tourism) now sit alongside more recent activities (mineral extraction, wind farms). However, protecting the resource base upon which these marine-related economic and social activities depend requires access to reliable and timely data. This requires both acquisition of background (baseline) data and monitoring impacts of resource exploitation on aquatic processes and the environment. Management decisions must be based on analysis of collected data to reduce negative impacts while supporting resource-efficient, environmentally sustainable uses. Multi-modal sensing and data fusion offer attractive possibilities for providing such data in a resource efficient and robust manner. In this paper, we report the results of integrating multiple sensing technologies, including autonomous multi-parameter aquatic sensors with visual sensing systems. By focussing on salinity measurements, water level and freshwater influx into an estuarine system; we demonstrate the potential of modelling and data mining techniques in allowing deployment of fewer sensors, with greater network robustness. Using the estuary of the River Liffey in Dublin, Ireland, as an example, we present the outputs and benefits resulting from fusion of multi-modal sensing technologies to predict and understand freshwater input into estuarine systems and discuss the potential of multi-modal datasets for informed management decisions